1. Field of the Invention
The subject invention relates generally to multi-layered metal gaskets for use in internal combustion engines.
2. Related Art
Multi-layered steel gaskets are traditionally used to form a seal between two mating components of a mechanical system or device, such as an internal combustion engine, to prevent leakage of combustion gases, cooling water, lubricating oil, or the like. Common applications involve placing a multi-layered steel gasket assembly between the engine block and cylinder head and between the engine block and exhaust manifold. Cylinder head gaskets typically extend around the cylinder bores of an engine to seal high-pressure combustion gases within the cylinder bores as well as seal oil and coolant passages. Exhaust manifold gaskets typically extend around the exhaust ports of an engine to seal high temperature exhaust gases flowing into the exhaust system. Once installed, the multi-layered steel gasket assembly bears the load from a bolted connection of the engine components and relies upon this load to provide an adequate seal therebetween.
Such prior art multi-layered steel gaskets typically have a plurality of steel gasket layers stacked in relation to one another including at least a first gasket layer and a second gasket layer. The first gasket layer and second gasket layer each have an inboard edge defining at least one aperture to be sealed. Each gasket layer also presents an outboard region radially spaced from the aperture. In cylinder head gasket applications, the aperture typically corresponds with cylinder bores of the internal combustion engine. Alternatively, in exhaust manifold gasket applications, the aperture typically corresponds with exhaust ports of the internal combustion engine. The gasket layers define at least one sealing bead between the inboard edge and the outboard region to provide an area of increase gasket thickness for greater sealing capability. Typically, the sealing bead extends annularly about each aperture.
Some of the prior art multi-layered gaskets further include a stopper layer disposed between the gasket layers. In accordance with U.S. patent application Ser. No. 11/812,113 to Umehara, the stopper layer may be welded to the outboard region of the first gasket layer at a weld joint. In accordance with U.S. Pat. No. 5,277,434 to Kestly et al., the stopper layer may extend from the outboard region of the gasket layers to the inboard edge of the gasket layers. At least one coating of sealing material may be applied between the gasket layers such that the coating is substantially coextensive with the plurality of gasket layers. Despite the presence of the coating, small combustion gas leaks can develop between the gasket layers and the stopper layer. This problem can occur because the stopper layer and the gasket layers do not directly contact the coating in the area immediately surrounding the apertures.